Mozilla Firefox 5 is the latest version of the Firefox web browser, released on June 21, 2011.This was the the first edition under the new faster-release regime Firefox kicked off in early 2011.New features

Even though the GUI has not been changed, Firefox 5 features:

Improved HTML 5 and CSS3 support
Improved overall performance
Visibility of Do-Not-Track option has been increased (disabling the ability for advertisers to track browsing habits and install cookies on the computer)
Stability and security improvements

How to install firefox 5 on ubuntu

Open the terminal and run the following commands

sudo add-apt-repository ppa:ubuntu-mozilla-security/ppa

or

sudo add-apt-repository ppa:mozillateam/firefox-stable

sudo apt-get update
sudo apt-get upgrade

Or if you are running ubuntu 11.04 you can try sudo apt-get upgrade it should install latest version of firefox.

It didn’t happen for me either. Turns out that software updates was disabled for some reason.

To check/fix this, open Ubuntu Software Center, select Edit => Software_Sources => Updates and check the checkboxes at “Important Security Updates” and “Recommended Updates”. Also, make sure that “Automatic Updates” is checked in the same view.

Okay this may be a bit wordy but it is what worked for me, maybe this will help someone with a similar problem. Running this Ubuntu version; {Ubuntu – Linux for Human Beings! You are using Ubuntu 10.04 LTS – the Lucid Lynx}

Steps 4., 5., and 6. are not really necessary but I’m a bit nerdy about leaving random bits and pieces of packages lying around.